Variable tuned transformer



Oct'. 13, 1942. H. A. MOORE ETAL VARIABLE TUNED TRANSFORMER Original Filed Aug. 12, 1937 2 Sheets-Sheet l FREQUENCY INCREASE Bnventor HAROLD AMO/FE /m/D J0 N B. MOORE Eg 7 SL@ 01AM-f Gtforneg oct; 13, 1942. H. A. MQORE HAL A 2,298,498

VARIABLE TUNED TRNSFORMER Original Filed Aug. 12, 1937 Z-Sheets-Sheet 2 3 n vento r www Anf/00,95 0F mss 8 ,li/v0 JO/f/v 5./1400/85 Gttomeg Patented Oct. 13, y194.2

VARIABLE TUNED TRANSFORMIB HaroldA.MoorcandJohnB.Moore,Biverhead,

assignorsto Radio Corporation of America, a corporation of Delaware application August 12, 1937, serial No. isa'isa Divided smi this application May s, me, sei-isi No. 333,092

lzClaims.

This invention relates to s new and novel arrangement of tuned transformers; and more particularly to tuned transformers having a variable band-width suitable for use in intermediate frequency ampiiiier systems of radio receivers.

Thisapplication is a division of my copending V application Serial No. 158,756, filed Aug. 12, 1937,` which is now Patent #2,208,041, issued on July 2.

1940, in which the claims are directed to the structural feature of theinvention, whereas this application contains claimsdirected to the circuit elements. A

The object of this invention is to-provide a simple means of obtaining two or more bandwidths. each having the optimum shape of selectivity characteristics, and each being centered around the same midband frequency.

Prior art methods of changing the band-width of tuned transformers have been such as to obltain the optimum shape of the frequency characteristics at only one value of band-width. Such adjustments were either inaccurate or laborious. The present invention makes it possible to quickly adjust the transformers. to give the optimum frequency characteristic at each of the two or more accurately predeterminedvalues of bandwidth'. Briey, the selection of the desired bandwidth in accordance with this inventionis accomplished by the` movement of a knob which' simultaneously sets the mutual induetance between the primary'and secondary to a predetermined value and either cts in or out additional damping resistance and timing capacitance. The object of cutting-in and out the preadjusted ilxed tuning capacitance and loading resistances is to make the constants of -the' circuit such that forV both conditions of band-width, the midband fre quency of the selected band will be constant and the Aresl'ionse curve will be essentially uniform (flat topped) throughout the useful pass band.

Fig. 5 is an underside elevation of Figs. 3 and 4 v Y in the intermediate frequency amplifiers of radio j This invention-will best beunderstood by re-v Q ferring to the accompanying drawings, in which:

Fig. l is a schematic circuit diagram of the v improved transformer arrangement;

Fig. 2 is a' diagram giving a graphie represen- 1 tation oi two band-widens;

Fig. 3 is a plan view of the apparatus-for accomplishing the purpose of this invention;

Fig. 4 is'a side view of Fig. 3, partly in section giving a longitudinal view of the coil coupling arrangement;

4A is a planview of a portion of Fig. 4 showing the variable andvilxed timing condenser arrangement; and

receivers, and is particularly adapted to what is known as commercial type receiving equipment. In this speelde embodiment of variable band-width intermediate frequency transformers, the band-width will not be continuously variable (although it is possible by a slight modification of the structure elements to make it so) but the construction will be such that a choice of two or more band-widths is available. :The electrical constants of the circuit for eachband-width are predetermined. Vacuum tube Al has its output connected to the primary coil Li of the intermediate frequency transformer M.- Connected in shunt withv coill Ll is a fixed capacity C, a trimming condenser C2, a resistance RI, nd a switch X` which is arranged to switch in an additional shunt resistance R2 and a capacitance C3. A secondary coupling coil L2 is shunted by a fixed capacitance C4, a trimming condenser C5 and terminating resistances R3 and R4. An additional shunt capacitance C3 and resistance R5 are shown as being capable of being switched in circuit by switch Y connected to the junction point of resistances R3 and RI, at which point a connection is made to the grid input of vacuum tube A2.

'I'he particular circuit arrangement shown `by Fig. 1 of the drawings provides the same voltage gain on both band-widths. This is accomplished by the combination of loading resistors RI, R2, R3, R4 and R5. In order to keep the characteristic centered around the same mid-band frequency F0, as shown in Fig. 2 of the drawings, 4

when the coupling between coils Ll and L2 is changed, the added capacitances C3 and CB are switched onto the primary and secondary circuits, respectively, at the same time as are the Referring now to Pigs. 3, 4 and 5, themechanv ical arrangement of the apparatus is shown. The circuit elements are all contained within a suitable shielding can l and are mounted upon a base of insulating material I. The fixed coil I isshownsupportedenbaseillyminsulating` rod l, which has one side cut away for mounting. The movable coil I is mounted upon an insulating rod l, which is cut away on both sides vto provide retention means for sliding engagement in a slot 1 of base I. To provide clearance space for the coils 3 and l, an aperture i is cut-out ofmemberl. Fixedcoilsupportrodlissecuredtobasez byapluralityofscrewsl and il fastened by nutsil and washers i2. Rod l is provided with a projecting guide piece Il which slides or telescopes within a bore Il rod l, ensuringperfectalignmentiorcoilslandl. plate il, also of insulating material. is fastened totheundersideofbasel. Thisplateservesthe also acts as a sub-base To limit the motion of l, two adiustable stop members I'I and il are provided. Stop member I1 is shown limiting the movementofcoiilinitsextremepositiomwhich limitstbecoillinitslooseeolmled'position. Stop member il limitscoil I in its close coupled position. Suitable pins il are provided for guiding members Il and Ilin slots Il, as shown. To vary the amount of movement of coil l, set screws 2l areloosened,andwhenthedeairedcoupling positions are secured, stops Il and il are securely'fas'tened in their respective positions by set screws 2i. Movement of member l and coil l is accomplished by a slotted stud 22. which is actuated by a shaft 2l and linked together by a spring member 24 which terminates in a spiral around shaft 23. A ball and socket arrangement 2l is secured to shaft Il and links together a second ball and socket arrangement 2l by a link 21.

A crank shaft 28 passes through abearing 2l, the

end of the shaft terminating in an operating knob 3l. A switchis provided for connecting in circuit resistance R2,`condenser CI, resistance R5 and condenser Cl. This switch is in the form of an insulating disc Il located on the lower end of shaft 23 having contact segments I! and il. Contacts 32 and 3l are arranged to connect together a plurality of, spring contact members 34 when the switch is rotated to the closed position, which is the position of maximum coupling. Other parts of the transformer comprise the variable condensers Il and Il, fixed condensers ll and 31, condensers Cl to C3 inclusive, and the Aassociated resistances RI to Rl, inclusive.

The operation of this improved tuned transformer is as follows: When control knob ll is turned, for example, from the narrow band to the wide band position, the following functions are performed.

(i) The coupling between coils I and l is increased by moving them closer together. increases the percentage coupling and mutual inductance to a predetermined value which is required for the wider band.

(2) Resistance R! is shunted'across a portion f of the secondary lcircuit terminating voltage divider, consisting of resistances R3 and R4, by means of switch Y, completing the between contact members N.` This compensates forthechangeingaincamedbythechangeof transformer impedance when the percentage coupling is changed. The total effective damping for the wide band is then made up by shunting cult by switch X completing the circuit between another pair of contact members 8l.

(3) Capacitances Cl and CI are switched on with the resistanc R8 and R2 as mentioned above. The added capacitances increase the effective total capacitance across each coil. The capacity of condensers CB and C3 are of such value as to make the frequency characteristic of the wide band position center about the same mid-band frequency, asin the case of the narrow band adjustment. These positions were previously described with reference to Fig. 2.

A further modification of this invention is that insteadof a choice of only two band-widths, as shown in the drawings, it is possible to provide three or more band-widths" by adding additional This another resistance R2 across the primary cir- 75 switch contacts and contact members; also, a detent action should be provided for the various coupling positions.y

What is claimed is: l

1. A tuned transformer having a variable frequency band width comprising an input and an output circuit, said transformer having a primary and a secondary coil in varying coupling relationship to each other, a fixed and variable condenser in shunt with each primary and secondary coil, an impedance element in shunt with said nxed and variable condensers, and means for simultaneously varying the coupling between said primary and said secondary coil, and for switching additional impedance elements in said input and output circuits for changing the band widths and maintaining the same mid-band frequency for all of said bands. i

2. A tuned transformer having a variable frequency band width comprising an input and an output circuit, said transformer having a primary and a secondary coil in varying coupling relationship to each other, a fixed and variable condenser in shunt with each primary and secondary coil. an impedance element in shunt with said ilxed and variable condensers, and means forv simultaneously varying the coupling between said primary and said secondary coil, and for switching resistance elements in said input and output circuits for changing the band widths and maintaining the same mid-band frequency for all of said bands.

3. A- tuned transformer having a variable frequency band width comprising an input and an output circuit, said transformer having a primary and a secondary coil in varying coupling relationship to each other, a ilxed and variable condenser in shunt with each primary and secondary coil, an impedance element in shunt with said xed and variable condensers, ana means for simultaneously varying the coupling between said primary and said secondary coil, and for switching capacitance elements in said input and output circuits for changing the band widths and maintaining the same mid-band frequency for all of said bands.

4. A tuned transformer having a variable frequency band width comprising an input and an output circuit, said transformer having a primary and a secondary coil in varying coupling relationship to each other, a fixed and variable condenser in shunt with each primary and secondary coii. an impedance element in shunt with said fixed and variable condensers, and means for simultaneously varying the coupling between said primary and said secondary coil, and for switching resistance and capacitance elements in said input and output circuits for changing the band widths and maintaining the same midband frequency for. all of said bands.

5. A tuned transformerhaving a variable frequency band width comprising an input and an output circuit, said transformer having a primary and a secondary coil in varying coupling relationship to each other, a fixed and variable condenser in shunt with each primary and secondary coil, a resistor in shunt with said fixed and variable condensers, and means for increasing the coupling between said primary and said secondary coils and simultaneously switching reactive elements in 'said input and output circuits for changing the band widths and maintaining the same mid-band frequency for all of said bands.

6. A tuned transformer having a variable frequency band width comprising an input and an output circuit, said transformer having a primary and a secondary coil in varying coupling relationship to each other, a fixed and variable condenser in shunt with each primary and secondary Veach other, a condenser shunting each of said coils, a resistor also in shunt tov each of said coils. a switch in circuit with each coll of said trans'- former and adapted in its closed position to connect an additional resistor in shunt to at least a portion of the associated coil, andunicontrol means for operating both of said switches and for simultaneously changing the coupling between said primary and secondary coils.

8. A transformer having a variable frequency band width comprising a primary coil and a secondary coll in varying coupling relation to each other, a condenser shunting each of said coils, a

resistor also in shunt to each of said coils, a

lswitch in circuit with each coil of said transformer and adapted in its closed position to connect lan additional condenser in shunt to `at least a portionof the associated coil, and unicontrol means for operating both o! said switches and for simultaneously changing the coupling between said primary and secondary coils.

9. A transformer having a variable frequency band width comprising a primary coil and a sec'- ondary coil in varying coupling relation to each other, a condenser shunting each of said coils, a resistor also in shunt to each of said coils, a circuit composed of a resistor shunted by a condenser associated with each of said coils, and a switch connected to each coil and` adapted in its closed position to shunt at least a portion of said coil by its associated circuit of resistor and shunt condenser, and unicontrol means for operating both of said switches and for simultaneously changing the coupling between said primary and secondary coils.

10. A transformer having a variable frequency band width comprising a primary coil and a secondary coil, means for tuning each coil of said transformer, a resistor in shunt to each of said coils, a switch in circuit with each coil of said transformer and adapted in its closed position lto connect an additional resistor in shunt to at least a portion of the associated coil, and unicontrol means for operating both of said switches and for simultaneously changing the coupling between said primary and secondary coils.

1l. A transformer having a variable frequency band width comprising a primary coil and a secondary coil. means for tuning each coil of said transformer, a resistor in shunt to each of said coils, a switch in circuit with each coil and adapted in its closed position to connect a condenser in shunt to at leastva portion of the associated coil, and unicontrol means for operating both of said switches-and for simultaneously changing the coupling between said primary and secondary coils.

12. A transformer having a variable frequency band width comprising a primary coil and asecondary coil, means for tuning each coil of said transformer, a resistor in shunt to each of said coils, a circuit composed ofa resistor shunted by a condenser associated with each of said coils, and a switch connected to each coil and adapted in its closed position to shunt atleast a portion of said coil by its associated circuit of resistor and shunt condenser, and unicontrol means for operating both of said switches and for simultaneously changing the coupling between said primary and secondary coils.

HAROLD A. MOORE. JOHN B. MOORE. 

